Downhole swivel

Abstract

A method and apparatus is disclosed which reduces or removes axial loads on the drive string of a rotary downhole pump, i.e. tensile loads due to the hydrostatic load of the pumped liquid on the pump rotor, and/or at least part of the weight of the drive string, or thrust loads caused during pressurized fluid injection operations by backpressure of injected fluid on the pump rotor. This substantially prevents drive string/production tubing friction, wear and/or buckle in downhole rotary pumping arrangements operated in straight or curved well bores. When used in connection with fluid production pumping arrangements, the apparatus reduces the friction between the drive string and the production tubing of a downhole rotary pump for the pumping of well fluids which pump has a pump rotor connected to the drive string and is operated in a well bore. When used in connection with fluid injection pumping arrangements, the apparatus prevents drive string buckle, especially in curved well bore situations. The apparatus includes a support for rotatably supporting the drive string in the production tubing at a location above the pump, and a fluid passage for permitting the pumped fluid to flow from the pump to a wellhead of the well. The support includes an axial load bearing structure for supporting, from the production tubing, at least part of an axial load on the drive string either generated by the hydrostatic load of a pumped liquid on the pump rotor or backpressure of injected fluid on the pump rotor. The fluid passage is shaped and constructed such that the pumped fluid can flow from the pump past the axial load bearing means to the wellhead. In fluid pumping applications, the apparatus can also be used to support at least part of the weight of the drive string to reduce the axial load on the drivehead.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 
     
       1. A downhole apparatus for use in a downhole rotary pumping arrangement which includes a downhole rotary pump having a pump rotor attached to and operated by a pump drive string rotatable in a production tubing and suspended from a drivehead, the apparatus being used for supporting on the production robing at least part of an axial load on the pump drive string, comprising: a support for rotatably supporting the drive string in the production tubing at a location between the pump rotor and the drivehead, the support including an axial load bearing means for rotatably supporting, on the production tubing, at least part of an axial load on the drive string caused by an axial load on the pump rotor; and   a fluid passage for permitting the pumped liquid to flow from the pump past the axial load bearing means and to a wellhead of the well.   
     
     
       2. A downhole apparatus as defined in claim 1 for reducing, in a well having at least one curved section, the friction between the drive string and the production tubing of the pump, wherein the support for rotatably supporting the drive string in the production tubing is shaped and constructed to be installed at a location between the curved section of the well bore and the pump, the axial load bearing means being adapted to rotatably support, from the production tubing, at least part of the tensile load on the drive string generated by the hydrostatic load of a pumped liquid on the pump rotor and at least part of the weight of the drive string. 
     
     
       3. The apparatus of claim 2, wherein the axial load bearing means supports the tensile load on the drive string generated by the hydrostatic load of the pumped liquid on the pump rotor, and at least part of the weight of the drive string. 
     
     
       4. The apparatus of claim 3, wherein the support has a cylindrical housing for connection to the production tubing and a hollow shaft for connection to the drive string, the hollow shaft being axially rotatably supported in the housing by a pair of radial bearings, and the load bearing means includes an annular bearing seat on and radially inwardly protruding from the housing, an opposingly positioned radially inwardly protruding load bearing flange on the shaft, and a thrust bearing positioned therebetween. 
     
     
       5. A downhole apparatus as defined in claim 1, wherein the support for rotatably supporting the drive string in the production tubing is shaped and constructed to be installed at a location adjacent the pump, and the axial load bearing means is adapted to rotatably support on the production tubing at least part of an axial thrust load on the drive string caused by backpressure of injected fluid on the pump rotor during pressurized fluid injection into the well. 
     
     
       6. The apparatus of claim 5, wherein the support has a cylindrical housing for connection to the production tubing and a hollow shaft for connection to the drive string, the hollow shaft being axially rotatably supported in the housing by a pair of radial bearings, and the load bearing means includes first and second thrust bearings respectively mounted between an annular bearing seat on and radially inwardly protruding from the housing and an opposingly positioned radially outwardly protruding load bearing flange on the shaft, the first thrust bearing being shaped and constructed to support axial thrust loads on the pump drive string and the second thrust bearing being shaped and constructed to support axial tension loads on the pump drive string. 
     
     
       7. The apparatus of claim 6, wherein the radial bearings are needle bearings and the first and second thrust bearings are a spherical roller thrust bearings. 
     
     
       8. The apparatus of claim 1, wherein the support has a cylindrical housing for connection to the production tubing and a hollow shaft for connection to the drive string, the hollow shaft being axially rotatably supported in the housing by a pair of radial bearings, and the fluid passage is provided by the interior of the hollow shaft and by a pair of fluid cross-over means for respectively connecting, at an end of the hollow shaft, the interior of the hollow shaft with an adjacent annular space between the tubing and the drive string. 
     
     
       9. The apparatus of claim 8, wherein each cross-over means is a cross-over member having an axis and including a solid shaft having an enlarged end, connecting means for coaxially attaching the enlarged end to one of the ends of the inner hollow shaft, an axial bore in the enlarged end, and at least one radial bore in the shaft and located behind the connecting means and communicating with the axial bore. 
     
     
       10. The apparatus of claim 9, wherein the radial bore is an oblique radial bore which encloses an acute angle with the axis of the cross-over member. 
     
     
       11. The apparatus of claim 10, wherein the cross-over member includes four oblique radial bores which are evenly distributed about the axis of the cross-over member and penetrate an outer surface of the member behind the enlarged portion. 
     
     
       12. The apparatus of claim 11, wherein the connecting means are shaped and constructed for releasable attachment of the enlarged end to one of the ends of the hollow shaft. 
     
     
       13. The apparatus of claim 5, wherein the radial bearings are friction bearings provided by opposing surfaces of the hollow shaft and bearing sleeves coaxially positioned in the housing, the opposing surfaces being provided with surface layers of respectively dissimilar metals selected for reducing friction and wear therebetween. 
     
     
       14. A fluid cross-over for providing fluid communication between an interior of a hollow shaft and an annular space surrounding the shaft and the cross-over, comprising a solid shaft having an axis and an enlarged end, attachment means for coaxially connecting the enlarged end to an end of the hollow shaft, an axial bore in the enlarged end, and at least two radial bores in the shaft for connecting the axial bore with the annular space, the radial bores being evenly spaced about the axis and penetrating an outer surface of the cross-over behind the enlarged end, the diameter of the radial bores being selected such that the torsional strength of the cross-over at the radial bores is at least equal to the torsional strength in the remainder of the cross-over. 
     
     
       15. A fluid cross-over as defined in claim 14, wherein the radial bores are oblique radial bores and the number and axial diameter of the bores is selected such that the sum of the cross-sectional areas of the bores is at least equal the cross-sectional area of the axial bore. 
     
     
       16. A fluid cross-over as defined in claim 14, wherein at any point through the radial bores the total cross-sectional area of the material of the cross-over is at least equal to the corresponding cross-sectional area at any other point of the cross-over. 
     
     
       17. A fluid cross-over for use in a downhole apparatus as defined in claim 8, comprising a solid shaft having an axis and an enlarged end, attachment means for coaxially connecting the enlarged end to an end of the hollow shaft, an axial bore in the enlarged end, and at least two radial bores in the shaft for connecting the axial bore with the annular space, the radial bores being evenly spaced about the axis and penetrating an outer surface of the cross-over behind the enlarged end, the diameter of the radial bores being selected such that the torsional strength of the cross-over at the radial bores is at least equal to the torsional strength in the remainder of the cross-over.